Laptop computers, tablets, mobile phones, and even large electric vehicles and robots, all have a rechargeable battery composed of several rechargeable battery sets linked in series or parallel with a certain working capacity. The rechargeable battery set is also composed of a number of rechargeable battery cells connected in series or parallel. As far as the battery set assembly factory is concerned, the rechargeable battery cells purchased may come from different vendors (even made by themselves). Specification (discharging capacity or discharging voltage) of the rechargeable battery cells might not differ. However, due to materials used, differences in detailed design, precision of processing or even different batches of manufacturing, performance, such as discharging capacity, of the rechargeable battery cells might fluctuate. Use of mixed lots of rechargeable battery cells in a rechargeable battery often causes battery unbalance after the rechargeable battery is assembled. It is inevitable in practice to use mixed rechargeable battery cells having different performance. Another example is an electrical vehicle powered by huge amount of battery sets. Since the number of rechargeable battery cells is more, maintenance of the battery sets is often carried out by replacing rechargeable battery cells with new ones so as to extend lifetime. If the replaced rechargeable battery cell is requested to have the same characteristics as other existing rechargeable battery cells, it is difficult. Management and measurement of the rechargeable battery under aforementioned problems are not easy.
Master-slave control is a method to take one device as a main device which is able to control or manage other linked devices. With the application of the method on battery management, it is able to achieve the effects of classified battery monitor and unified data processing. It is a good way to manage and measure the rechargeable battery cells by distinguishing them into a master and slaves according to some characteristics. Related technique has been disclosed by the U.S. Pat. No. 7,453,236. Please refer to FIG. 1 and FIG. 2. FIG. 1 illustrates a multi-battery set system of the technique. The system includes a master battery set 100 and a first to a Nth slave battery sets 101˜10N. The master battery set 100 and the first to Nth slave battery sets 101˜10N are linked in series to the power outputs V+ and V− and output a predetermined power to the power outputs V+ and V−. The master battery set 100 and the first to Nth slave battery sets 101˜10N have the same configuration. It is only in the difference of roles of master and slave. Therefore, only one battery set is illustrated.
Please refer to FIG. 2. When a battery set is set as a master battery set, a controller 200 of the battery set receives a total voltage value from the first to Nth slave battery sets 101˜10N and a battery voltage and current detecting circuit 202 receives a total voltage value from a battery string 204 (with 8 battery cells linked in series inside). Then, the controller 200 calculates a target total voltage value of the whole the battery set and pass it to the first to Nth slave battery sets 101˜10N to control a switch unit 206 according to the target total voltage value. Meanwhile, when others are set as slave battery sets, the controller 200 sends a total voltage value of itself according to the request from the master battery set 100 and control the switch unit 206 according to the target total voltage value provided by the master battery set 100. A switch unit controller 208 inside the switch unit 206 controls on/off of a charging switch element 2081 and a discharging switch element 2082 according to the target total voltage value in different charging and discharging stages, respectively. The system uses a driving signal to operate the controller 200. The controller 200 and other battery set are connected in a communicating path which conforms to the specification of RS232.
The most special feature of the '236 is the way it chooses the master battery set. The way is to let each battery set to judge if the voltage signal in the communication line is at high level or low level during a first desired time when they are just initiated or receive a setting master battery signal. If the signal is at the low level, it means other battery sets want to be the master battery set. Then, each battery set sets itself as a slave battery automatically when it receives another setting master battery signal indicating which one is the master battery set. Otherwise, if the signal is at the high level, it means other battery sets don't want to be the master battery set. Then, any one of the battery sets sends a low level voltage signal during a second desired time and a high level voltage signal after the second desired time lapses. If one battery set finds out that all the signals received from the communication line is at the high level after it sent out the high level voltage signal, it means all other battery sets don't want to be the master battery after querying, then the battery set sets itself as the master battery set automatically and sends the mentioned setting master battery signal indicating which one is the master battery set to other battery sets. It is conceivable that if all battery sets send the high level voltage signal after the second desired time lapses, is it possible to confirm which one is master battery set? In order to settle such special condition, '236 has set different second desired time for each battery set. It means the choice of master battery set has priority differences without considering the environmental variability and signal transmission problems in the case.
The patent mentioned above has provided a good example of master-slave control technique. With application of master and slave battery sets, a single window is provided for administration so that calculation of total voltage can be done by the master battery set for all the battery sets and then fed back to each slave battery set. It is advantageous that it is easy to control charge or discharge of each battery set when the whole battery set system charges or discharges in case the problems such as over-charge and over-discharge.
However, according to the battery set system in the patent, the role of the master battery set is not assigned by turns for every battery set. It is easy to excessively rely on some battery set and cause burden for that battery set so as to consume related managing element and reduce its lifetime. Meanwhile, as to the priority of master battery set has been defaulted. If the managing element has problem to work, operation of the whole system will be affected. Last, the system can only detect voltage value. Other data related to power capacity can not be available through the system. About the defects mentioned above, it is desired for the related industry to find out so that a better battery set system and battery management system can be provided.